1. Field of the Invention
The present invention relates to a transmission system of a hybrid electric vehicle, and more particularly, to a transmission system of a hybrid electric vehicle that implements an electric vehicle (EV) mode, a continuous mode, and a parallel mode of direct-coupling driving and overdrive (OD) driving.
2. Description of the Related Art
In general, a hybrid electric vehicle is a vehicle that is driven by efficiently combining two or more different types of power sources.
The hybrid electric vehicle generally uses an engine and a motor/generator, and uses as a primary power source a motor/generator having a relatively excellent low-speed torque characteristic at a low speed and uses as the primary power source an engine having a relatively excellent high-speed torque characteristic at a high speed.
As a result, the hybrid electric vehicle is excellent in fuel efficiency enhancement and reduction of exhaust gas because an operation of the engine using fossil fuel stops and the motor/generator is used at a low-speed section.
A transmission system of the hybrid electric vehicle is classified into a single-mode scheme and a multiple-mode scheme.
The single-mode scheme has an advantage that torque transmission mechanisms such as a clutch and a brake for transmission control are not required, but disadvantages that when the vehicle travels at a high speed, efficiency deteriorates, and as a result, the fuel efficiency is low and an additional torque increasing device is required to apply the single-mode scheme to large-sized vehicles.
The multiple-mode scheme has advantages that when the vehicle is driven at the high speed, the efficiency is high and torque can be designed to increase, and as a result, the multiple-mode scheme can be applied to large and medium-sized vehicles.
As a result, in recent years, the multiple-mode scheme has primarily been adopted rather than the single-mode scheme and the resulting research has been actively conducted.
The multiple-mode scheme power transmission system is configured to include a planetary gear set, a plurality of motors/generators used as the motor and the generator, a torque transmission mechanism capable of controlling rotation elements of the planetary gear set, a battery used as power sources of the motors/generators, and the like.
The multiple-mode scheme power transmission system has different operating mechanisms according to connection configurations of the planetary gear sets, the motors/generators, and the torque transmission mechanisms.
In addition, since the multiple-mode scheme power transmission system has characteristics that durability, power transmission efficiency, a size, and the like depend on the connection configurations, research and development for implementing a power transmission structure which is stronger has small power loss, and is compact has been continued in a transmission system field of the hybrid electric vehicle.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.